(1) Field of the Invention
The present invention relates to a method for fabricating lateral junction semiconductor devices. More specifically, the present invention is concerned with a method for fabricating lateral junction optoelectronic semiconductor devices, and in particular solid state single photon source (SPS) devices.
(2) Description of the Art
Conventional, or vertical, light emitting p-n junctions are difficult to integrate with planar devices such as transistors or resistors. Lateral p-n junctions are not only easier to combine with other devices, but may also have superior characteristics. For example, in laser diodes, electrons and holes are injected into the active area through higher band-gap layers, which provide optical confinement. This limits the modulation bandwidth as the carriers have an unnecessary excess energy, which increases their radiative recombination time. Additional advantages of lateral junctions include smaller junction area and junction capacitance, and co-planar contacts.
An example of an optoelectronic device based on a lateral p-n junction configuration is the solid state single photon source (SPS) described in patent GB2354368.
A variety of conventional approaches for fabricating lateral p-n junctions exist. For example, devices based on the amphoteric nature of silicon in gallium arsenide (GaAs), where the silicon either gives n-type or p-type doping depending on the substrate orientation, are known (D. L. Miller, Appl. Phys. Lett. 47, 1309 (1985) refers). Several groups have reported luminescence in such devices. See for example the following references:
T. Saiki, S. Mononobe, M. Ohhtsu, N. Saito, and J. Kusano, Appl. Phys. Lett. 67, 2191 (1994).
P. O. Vaccaro, H. Ohnishi, and K. Fujita, Appl. Phys. Lett. 72, 818 (1982).
A. North, J. Burroughes, T. Burke, A. Shields, C. E. Norman, and M. Pepper, IEEE J. Quantum Electron. 35, 352 (1999).
However, this technique is complicated, as it requires the growth, selective removal, and re-growth of semiconductor material.
Focused Ion Molecular Beam Epitaxy has also been suggested as a technique for fabricating lateral junctions but, in common with the technique described above, is complicated and requires specialist equipment (see P. J. A. Sazio, S. Vijendran, W. Yu, H. E. Beere, G. A. C. Jones, E. H. Linfield, and D. A. Ritchie, J. Crystal Growth 201/202, 12 (1999)).
More recently, Kaestner et. al. have reported a method of forming a lateral p-n junction in an undoped, low band gap channel (Jpn. J. Appl. Phys., Part 1 41, 2513 (2002), and Microelectron. Eng. 67-68, 797 (2003) refer). Carriers of both types are introduced into the channel from either side via doped high band gap layers that are parallel to the surface. In the as-grown state, one carrier type is fully depleted, whereas if the upper highly doped region is removed by etching, the carrier type that was previously depleted collects at the interface between the high and low band gap layers. A p-n junction in the low band gap channel therefore forms below the edge of the etched region.
A similar scheme was reported by Cecchini et. al. (M. Cecchini, V. Piazza, F. Beltram, M. Lazzarino, M. B. Ward, A. J. Shields, H. E. Beere, and D. A. Ritchie, Appl. Phys. Lett. 82, 636 (2003)), except that the low band gap channel was initially doped p-type via a doped high band gap layer parallel to the surface. A region of the doped high band gap layer was then etched away, and an n-type contact was evaporated to give an n-type region in the low band gap channel.
However, both of these schemes rely on accurate etching of the doped layers so that the channel itself isn't either destroyed or fully depleted.